Research on anti-fatigue design method of welded structure oriented to stiffness coordination strategy

PurposeIn order to obtain the relationship between the geometry and stress concentration of load-bearing welded joints, the fatigue design method of welded structures based on stiffness coordination strategy is studied.Design/methodology/approachBased on the structural stress theory, a new method for anti-fatigue design of welded structures oriented to stiffness coordination strategy is proposed, and the detailed implementation process of this method is given. This method is also called the three-stage anti-fatigue design method for welded structures, which includes three stages, namely, identification, analysis and relief of stress concentration.FindingsThrough the experimental analysis of welded joints in IIW standard, the effectiveness of stiffness coordination in welded joint design is proved. The method is applied to the design of welded parts and products, and the feasibility of the method in alleviating the phenomenon of stress concentration and improving the fatigue resistance of welded structures is verified.Originality/valueIn this study, based on the principle of coordinated design of weld stiffness, a three-stage anti-fatigue design method of welded structure is proposed. The method has practical value for the optimization design and anti-fatigue performance improvement of welded structure in engineering products.

Advanced Trends in Metallurgy and Weldability of High-Strength Cold-Resistant and Cryogenic Steels

Thermomechanical Controlled Processing (TMCP), the initial microstructure and mechanical properties of rolled products made of high-strength steels, have a significant influence on the properties and reliability of welded structures for low temperature and cryogenic service. This paper systematizes advanced research trends in the field of metallurgy and weldability of high-strength cold-resistant and cryogenic steels. The classification and properties of high-strength steels are given and TMCP diagrams and phase transformations are considered. Modern methods of improving the viscoplasticity of rolled steel and welded joints are analyzed. The problems of the weldability of high-strength steels are reduction of impact toughness at low temperatures, hydrogen embrittlement, anisotropy, and softening of welded joints in the heat-affected zone. The authors propose a systemic concept and methods for improving the metallurgy and weldability of high-strength steels for low temperature and cryogenic service.

Study on Fatigue Performance of Non-Uniform Thickness Markless Laser Lap Welding

In this paper fatigue properties of three groups of unequal thickness unmarked overlap laser welding of the external wallboard connected of type A and B vehicle were studied. In addition, a group of overlap penetration welded structures of 1.5mm-301L-HT+0.8mm-301L-DLT is designed to study the impact of penetration rate to the mechanical properties. The influence of the weld geometry and plate combination on fatigue fracture behavior and fatigue property is studied based on the combination of fatigue test and simulation stress analysis. Fatigue studies have shown that in spite of the thickness of the two lap unequal thickness welded plate is disparities -- unmarked non-penetration welding outer plate is thicker but it appears fatigue fracture on the outer plate. The safety fatigue limit of three different non-penetration welded structures of plate combinations and weld structures is close which further proofs that the stress state and microstructure of non-penetration outer plate is not conducive to fatigue fracture. It is consistent with the results of the finite element simulation. The fatigue limit of lap welded structure increase with the increase of plate thickness.

Duplex Steels Used in Building Structures and Their Resistance to Chloride Corrosion

Welded structures made of duplex steels are used in building applications due to their resistance to local corrosion attack initiated by chlorides. In this paper, the material and technological factors determining the corrosion resistance are discussed in detail. Furthermore, recommendations are formulated that allow, in the opinion of the authors, to obtain a maximum corrosion resistance for welded joints. The practical aspects of corrosion resistance testing are also discussed, based on the results of qualification tests. This work is of a review character. The conclusions and practical recommendations are intended for contractors and investors of various types of structures made of the duplex steel. The recommendations concern the selection and use of duplex steels, including the issues of metallurgy, welding techniques, and corrosion protection.